NHibernate JoinAlias查询与null测试无法正常工作

Question

我在NHibernate中使用JoinAlias QueryOver获得了一些意想不到的行为.

我的实体基本上是这样的:

public class Field
{
    public virtual long Id { get; protected set; }
    public virtual Field Parent { get; protected set; }
    public virtual FieldType Type { get; protected set; }
    public virtual string Value { get; protected set; }

...(Ctors etc
}

我的映射是这样的:

public class FieldMap : ClassMap<Field>
{
    public FieldMap()
    {
        Id(x => x.Id)
            .GeneratedBy.Native();

        References(x => x.Type)
            .Column("FieldTypeId")
            .LazyLoad()
            .Cascade.All()
            ;

        Map(x => x.Value);

        References(x => x.Parent)
            .Column("ParentFieldId")
            .Nullable()
            .LazyLoad()
            .Cascade.All()
            ;
    }

我的查询:

        Field fieldAlias = null;
        string typeAlias = null;
        Field parentFieldAlias = null;

        var query = getSession().QueryOver<Field>(() => fieldAlias)
            .JoinAlias(() => fieldAlias.Type, () => typeAlias)
            .Where(() => typeAlias.Name == type)
            .JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
            .Where(() => (parentFieldAlias.Value == parentValue) || (parentFieldAlias == null))
            ;

就我而言,这应该给我一些像这样的SQL:

... WHERE(a.ParentFieldId == NULL)OR(a.ParentFieldId = c.FieldId AND c.Value = parentValue)

但我得到一个空引用异常.(我假设当别名被解析且Parent为null时).

例外细节是:

System.NullReferenceException occurred
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=NHibernate
  StackTrace:
       at NHibernate.Criterion.ConstantProjection..ctor(Object value)
       at NHibernate.Criterion.Projections.Constant(Object obj)
       at NHibernate.Impl.ExpressionProcessor.FindMemberProjection(Expression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(Expression left, Expression right, ExpressionType nodeType)
       at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(BinaryExpression be)
       at NHibernate.Impl.ExpressionProcessor.ProcessBinaryExpression(BinaryExpression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessOrExpression(BinaryExpression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessBinaryExpression(BinaryExpression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessLambdaExpression(LambdaExpression expression)
       at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression`1 expression)
       at NHibernate.Criterion.QueryOver`2.Add(Expression`1 expression)
       at NHibernate.Criterion.QueryOver`2.Where(Expression`1 expression)
       at NHibernate.Criterion.QueryOver`2.NHibernate.IQueryOver<TRoot,TSubType>.Where(Expression`1 expression)
       at Ismoos.Director.FieldOptionsQuery.Execute(Service service, String type, String parentValue) in D:\Work\Ismoos\Ismoos\Director\Ismoos.Director\FieldOptionsQuery.cs:line 31
  InnerException:

我尝试了几种不同的方式,包括:

            .JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
            .Where(Restrictions.Or(Restrictions.On(() => fieldAlias.Parent).IsNotNull,
                Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue))))

但这些都不起作用.

我有一个解决方法,通过省略查询中父字段值的限制,并在QueryOver返回后执行LINQ查询,如下所示:

        Field fieldAlias = null;
        string typeAlias = null;
        Field parentFieldAlias = null;

        var query = getSession().QueryOver<Field>(() => fieldAlias)
            .JoinAlias(() => fieldAlias.Type, () => typeAlias)
            .Where(() => typeAlias.Name == type)
            ;

        var list = query
        .List<Field>()
        ;

        return list
            .Where(x => (x.Parent == null) || (x.Parent.Value == parentValue))
            .ToList();

但这并不像在QueryOver中那样优化.

有什么建议？

Answer 1

有限制的第二个解决方案可以胜任.有两个问题.我们需要LEFT JOIN到Parent,我看到一个错字:IsNotNull应该是IsNull正确评估OR声明:

破解IsNotNull(最有可能是内连接)

.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias)
.Where
(
  Restrictions.Or(
    Restrictions.On(() => fieldAlias.Parent).IsNotNull, // here
    Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue)))
)

工作OR与IsNull和LEFT JOIN:

.JoinAlias(() => fieldAlias.Parent, () => parentFieldAlias
           , NHibernate.SqlCommand.JoinType.LeftOuterJoin)) // left join for NULL
.Where
(
  Restrictions.Or(
    Restrictions.On(() => fieldAlias.Parent).IsNull, // this is what we need
    Restrictions.On(() => parentFieldAlias.Value).IsLike(parentValue))
);

第一个解决方案的问题是,我们无法评估浮点/虚拟对象的 null :parentFieldAlias

.Where(()=>(parentFieldAlias.Value == parentValue)|| (parentFieldAlias == null));

我们需要检查所有者的财产: fieldAlias.Parent